With an increase in the precision of a semiconductor exposure apparatus, a vibration isolation/suppression apparatus with higher performance has been required. In a semiconductor exposure apparatus, in particular, it is required to prevent vibrations that affect exposure from being produced in an exposure stage or a structure forming an exposure apparatus body. For this purpose, the exposure apparatus body must be insulated from external vibrations, including vibrations from an apparatus mount pedestal such as a floor, as much as possible, and vibrations produced when equipment, having a driving means such as an X-Y stage mounted on the apparatus main body, operates, must be quickly reduced.
If structural resonance vibrations are produced in apparatus/equipment mounted on the exposure apparatus body, and a sufficient damping property is not ensured, these resonance vibrations must also be effectively reduced/suppressed to prevent them from affecting the apparatus performance.
In the semiconductor exposure apparatus, in particular, the intermittent, repetitive operation, called step-and-repeat, of the exposure stage apparatus or scanning operation for scanning exposure excites vibrations, in the apparatus body. The drive reaction force generated by the stage apparatus and the load movement of the stage apparatus excite vibrations in equipment or a structure that forms the apparatus body. For a vibration isolation/suppression apparatus in this field, therefore, it is essentially required to insulate the apparatus body from external vibrations including vibrations from an apparatus mount pedestal such as a floor, and to effectively reduce/suppress rigid-body vibrations and resonance vibrations produced in the apparatus body when the equipment mounted on the apparatus body operates. In a scan exposure apparatus, in particular, since exposure is performed while an exposure stage apparatus performs a scanning operation, severe requirements are imposed on vibration reduction/suppression performance. Therefore, a vibration isolation/suppression apparatus with higher performance becomes indispensable.
To satisfy such a requirement, various types of active vibration isolation/suppression apparatuses have been developed and put into practice, which detect the vibrations of a vibration isolation base on which a semiconductor exposure apparatus is mounted by using a sensor, to compensate for the resultant detection signal for the vibrations, and to feed back the resultant signal to each actuator for applying a control force to the vibration isolation base, thereby actively suppressing vibration.
As a conventional vibration isolation/suppression apparatus for a semiconductor exposure apparatus, an active vibration isolation apparatus based on the vibration isolation leg scheme for reducing/suppressing the vibrations of the vibration isolation base by using a support mechanism for vibration-suppressing/supporting the vibration isolation base has been widely used. More specifically, a vibration isolation apparatus has been widely used, which controls the vibrations of the vibration isolation base by using actuators formed by air springs for supporting the vibration isolation base on an apparatus mount pedestal or a combination of such air springs and electromagnetic actuators that are placed dynamically parallel to the air springs to apply a control force between the vibration isolation base and the apparatus mount pedestal.
An active vibration isolation apparatus of this type and a semiconductor exposure apparatus using this vibration isolation apparatus are disclosed in “Vibration Isolation Apparatus, Exposure Apparatus and Device Manufacturing Method using the Same, and Vibration Isolation Method”, Japanese Patent Laid-Open No. 11-294520 proposed by the present applicant. According to this prior art, an active vibration isolation apparatus configured to reduce/suppress the vibrations of a vibration isolation base is disclosed, which uses air springs, as air actuators, which support the vibration isolation base on an apparatus mount pedestal, and also uses electromagnetic linear motors for applying a control force between the vibration isolation base and the apparatus mount pedestal. In this apparatus, each actuator is controlled on the basis of a signal obtained by detecting any displacement, acceleration, or the like, of the vibration isolation base using a sensor and performing a compensation computation for the signal, such as a signal being obtained by compensating for a signal from equipment having a driving means such as an X-Y stage mounted on the vibration isolation base, a signal being obtained by detecting the vibrations of the apparatus mount pedestal and performing a compensation computation for the resultant signal, or the like. This apparatus realizes excellent vibration isolation/suppression performance, which the active vibration isolation apparatus based on the pneumatic driving scheme widely used in the past does not have, by respectively allocating control functions to air actuators capable of easily obtaining a large thrust and electromagnetic actuators with excellent response properties in consideration of the merits of the two types of actuators.
An active vibration suppression apparatus, called an active mass damper or a countermass, tends to be used in the field of precision vibration control as well, which is designed to perform vibration control more finely than such an active vibration isolation apparatus based on the vibration isolation leg scheme and to realize more sophisticated vibration isolation/suppression control by driving an inertial load serving as a weight by using an actuator and using the resultant drive reaction force as a control force.
Such conventional active vibration suppression apparatuses are disclosed in “Active Vibration Suppression Apparatus and Semiconductor Exposure Apparatus Using the Same”, Japanese Patent Application No. 11-151141 filed by the present applicant, “Stage Apparatus, Exposure Apparatus using the Same, and Device Manufacturing Method”, Japanese Patent Laid-Open No. 11-190786, “Active Vibration Suppression Apparatus”, Japanese Patent Application No. 2000-122731 filed by the present applicant, and the like. Methods and apparatuses for reducing/suppressing vibrations are also disclosed in these references.
FIG. 17 is a perspective view for explaining the structure of a vibration suppression apparatus proposed as “Active Vibration Suppression Apparatus and Semiconductor Exposure Apparatus Using the Same”, Japanese Patent Application No. 11-151141. This vibration suppression apparatus is configured to drive a mass serving as a weight in the straight direction by using an actuator for generating a thrust in the straight direction. The apparatus shown in FIG. 17 suppresses vibrations in the vertical direction.
This apparatus is comprised of a linear-acting actuator 81 such as an electromagnetic linear motor and an inertial load 82 driven by the linear-acting actuator 81 in the straight direction. FIG. 17 shows an example of the apparatus using an electromagnetic linear motor as a linear-acting actuator, which generates a thrust in the straight direction indicated by the arrow in FIG. 17 by the interaction between a stator 81a having a coil winding and a movable part 81b fixed to the inertial load 82 and having a permanent magnet. The linear-acting actuator 81 is fastened to a vibration suppression target through a base member 83 and generates a thrust to displace the inertial load 82 with respect to the vibration suppression target. When the linear-acting actuator 81 is caused to generate a thrust to displace the inertial load 82, the reaction force of the thrust acting on the inertial load 82 acts on the vibration suppression target.
FIG. 18 shows an example of the structure of a vibration suppression apparatus that acts to reduce vibrations in the horizontal direction by a similar method. Like the apparatus shown in FIG. 17, this apparatus is comprised of a linear-acting actuator 84 such as an electromagnetic linear motor, an inertial load 85 driven in the straight direction by the linear-acting actuator 84, and the like. FIG. 18 shows an example of the apparatus using an electromagnetic linear motor as a linear-acting actuator, which generates a thrust in the straight direction indicated by the arrow in FIG. 18 by the interaction between a stator 84a having a coil winding and a movable part 84b fixed to the inertial load 85 and having a permanent magnet. The linear-acting actuator 84 is fastened to a vibration suppression target through a base member 86 and generates a thrust to displace the inertial load 85 with respect to the vibration suppression target. When the linear-acting actuator 84 is caused to generate a thrust to displace the inertial load 85, the reaction force of a thrust acting on the inertial load 85 acts on the vibration suppression target.
An active vibration suppression apparatus of this type uses such a reaction force as a control force for a vibration suppression target, and adjusts the control force on the basis of a signal obtained by compensating for a detection signal representing the vibrations of the vibration suppression target, thereby performing vibration control. That is, unlike an active vibration isolation apparatus based on the vibration isolation leg scheme, this apparatus can reduce the vibrations of a vibration isolation base or equipment without applying any unnecessary force as the reaction force of a control force for vibration control to a portion outside the apparatus. This apparatus, therefore, has the merit of preventing the reaction force of a force for the reduction/suppression of vibrations from exciting vibrations in an apparatus mount pedestal or peripheral environment, which cause vibrations affecting precision equipment mounted on the vibration isolation base.
An apparatus of this type is configured to obtain a force acting on a vibration suppression target from a drive reaction force of an inertial load in a vibration suppression unit instead of being generated between external equipment and a vibration suppression target. If, therefore, the vibration suppression apparatus can be manufactured into an appropriate shape, a vibration suppressing effect can be obtained by locating the apparatus to a place where a dashpot used to reduce the structural resonance vibrations of equipment or a reinforcing member for ensuring rigidity cannot be installed.
In actually using an active vibration suppression apparatus of this type for applying a control force to a vibration suppression target by using a linear-acting actuator, an inertial load and its movable stroke must be appropriately designed in consideration of a control force necessary for the reduction of vibrations, the frequency band of vibrations to be suppressed, and the like.
Assume that the vibrations of a vibration suppression target which originate from the drive reaction force produced by equipment such as an X-Y stage are reduced by using an active vibration suppression apparatus of the type described above with reference to FIGS. 17 and 18. In this case, to obtain a control force required to suppress vibrations, an apparatus having an inertial load mass and a movable stroke equal to or similar to those of the X-Y stage must be used. However, since an allowable space is limited, a mass and movable stroke sufficient to obtain a predetermined vibration suppressing action and effect may not be ensured.
Assume that vibrations to be suppressed by an active vibration suppression apparatus of this type are the resonance vibrations of a structure having a relatively high resonance frequency, and a large mass or stroke are not required to suppress the vibrations of the structure itself. Even in this case, if equipment such as an X-Y stage operates on a surface plate, or the like, rigidly fastened to a vibration suppression target, a vibration isolation base on which the X-Y stage, and the like, are mounted vibrates at a low frequency corresponding to the natural frequency of a vibration system constituted by support legs of the vibration isolation base. As a consequence, the structure as the vibration suppression target also vibrates at the low frequency. In such a case, due to the influence of the low-frequency vibrations produced in the vibration isolation base and the structure as the vibration suppression target, the inertial load as a part of the active vibration suppression apparatus may greatly swing and operate beyond its movable stroke.
If the stroke of the inertial load is limited due to such restrictions on the specifications of the structure of the vibration suppression apparatus, the generation of vibrations of frequency components other than the control target, or the like, may prevent a sufficient vibration suppressing effect from being obtained. Furthermore, the inertial load may collide with a member such as a stopper, which is placed to prevent the inertial load from exceeding the stroke range. This may create a large shock to the vibration suppression control system, resulting in a control operation failure. In contrast to this, if the control gain is suppressed to prevent an inconvenience caused by stroke over, a necessary control effect cannot be ensured.
Under these circumstances, an active vibration isolation apparatus based on the vibration isolation leg scheme that has been widely used in a semiconductor exposure apparatus, and the like, is configured to apply a control force to a vibration isolation base or a member rigidly fastened to the base. That is, the apparatus is configured to reduce/suppress the vibrations of the vibration isolation base or surface plate on which various types of equipment constituting an exposure apparatus are mounted. In this case, if equipment and structures are rigidly fastened to the vibration isolation base or surface plate, and no structural resonance occurs, the vibrations of the mounted equipment and structures can be satisfactorily reduced/suppressed by the vibration isolation apparatus based on the vibration isolation leg scheme.
In many cases, in an actual apparatus, however, structural resonance vibrations are produced in mounted equipment and structures due to various restrictions on equipment design, and a satisfactory damping property cannot be provided for the resonance vibrations. In addition, when heavy equipment and structures are fastened to the vibration isolation base or surface plate, a spring/mass system may be formed due to insufficient fastening rigidity, and vibrations may be produced at a level that cannot be neglected in ensuring satisfactory apparatus performance.
When such vibrations are produced in a mounted equipment and structures, even if the vibrations of the vibration isolation base or surface plate are reduced/suppressed, those of these equipment and structures cannot be sufficiently suppressed. This affects the precision of the apparatus and degrades the exposure performance. In a semiconductor exposure apparatus, in particular, some structure needs to have a cantilever support structure in terms of equipment layout design, and swinging vibrations are produced around the fulcrum of the structure, affecting the performance of the semiconductor exposure apparatus.
The vibrations of mounted equipment/structure of this type can be reduced/suppressed by interposing a dashpot for providing a damping property between the external equipment and the vibration suppression target or by attaching a reinforcing member for ensuring rigidity. However, such a member cannot be attached because of restrictions on the equipment layout design in many cases. For this reason, vibrations such as structural resonance of equipment/structure cannot be sufficiently suppressed, and such vibrations often become big factors that hinder an improvement in the performance of a semiconductor exposure apparatus. Therefore, demands have arisen for a means/method of effectively reducing/suppressing (i) rigid-body vibrations and structural resonance of equipment/structures having severe restrictions on the layout design, and for a semiconductor exposure apparatus having the means/method.
In addition, with an increase in the precision of a semiconductor exposure apparatus, it is required to further reduce the influence of environmental vibrations of an apparatus mount pedestal, and the like. In order to meet such a requirement, a control method has been proposed and applied to the above active vibration isolation apparatus based on the vibration isolation leg scheme, which compensates for a detection signal representing the vibrations of an apparatus mount pedestal for these vibrations and feeding forward the resultant signal to an actuator for applying a control force to a vibration isolation base. According to this method, the actuator is made to generate a control force to cancel out vibrations transmitted from the apparatus mount pedestal to the vibration isolation base through vibration isolation legs on the basis of a detection signal representing the vibrations of the apparatus mount pedestal. This method can reduce/suppress the amount of vibrations transmitted from the apparatus mount pedestal much more than the control scheme using only a detection signal representing the vibrations of the vibration isolation base.
This control operation is, however, performed by using a detection signal representing the vibrations of a floor or apparatus mount pedestal, i.e., a detection signal representing a physical quantity including many uncertainties in terms of the generation mechanism of vibrations. For this reason, owing to various uncertainties acting in an apparatus mount environment, unpredictable, uncertain signals may be fed forward to the control system. That is, this control method has a weak point in the reliability of vibration control operation.
Such a problem can be effectively solved by a method of reducing vibrations transmitted to the exposure apparatus body by suppressing the vibrations of a structure itself on the apparatus pedestal on which the semiconductor exposure apparatus is installed. In consideration of such a point as well, demands have arisen for a means/method of reducing/suppressing vibrations of types that are not suited to a vibration isolation apparatus based on the vibration isolation leg scheme.
In the prior art associated with Japanese Patent Application No. 11-151141, and the like, there is no detailed description about a vibration suppression method and an apparatus aimed at removing the vibrations of a structure as a part of a semiconductor exposure apparatus, more specifically, the vibrations of a cantilever support structure as a part of a semiconductor exposure apparatus, a structure on the mount pedestal side on which vibration isolation legs for vibration-isolating/supporting a semiconductor exposure apparatus are mounted, and the like, as in the apparatus according to the present invention. In “Active Vibration Suppression Apparatus”, Japanese Patent Application No. 2000-122731, and Japanese Patent Laid-Open No. 11-190786, a vibration suppression apparatus for a semiconductor exposure apparatus is described. Basically, however, such references are limited to the disclosure of vibration suppression methods and apparatuses aimed at suppressing rigid-body vibrations such as the vibrations of a vibration isolation base or surface plate as a part of an exposure apparatus body.